Relative density is compared by evaluating its value in relation to a reference density (typically water).
Here's how to interpret relative density:
- Relative Density < 1: The substance is less dense than the reference material. It will float on the reference material if immiscible.
- Relative Density > 1: The substance is more dense than the reference material. It will sink in the reference material if immiscible.
- Relative Density = 1: The substance has the same density as the reference material. Equal volumes of the two substances have the same mass, and neither will sink nor float in the other (if immiscible, it will remain suspended).
Understanding Relative Density
Relative density (also known as specific gravity) is a dimensionless number that compares the density of a substance to the density of a reference substance, usually water at 4°C (which has a density of approximately 1000 kg/m³ or 1 g/cm³).
Formula:
Relative Density = (Density of Substance) / (Density of Reference Substance)
Practical Implications
Understanding relative density has numerous practical applications:
- Determining if an object will float or sink in water: This is crucial in naval architecture, maritime engineering, and even everyday life.
- Quality control in manufacturing: Deviations in relative density can indicate impurities or inconsistencies in a product.
- Geological surveys: Relative density measurements help identify different rock types and mineral compositions.
- Clinical diagnostics: Urine specific gravity is a common test used to assess kidney function.
Examples
| Substance | Density (kg/m³) | Relative Density (Water at 4°C as reference) | Comparison to Water |
|---|---|---|---|
| Ethanol | 789 | 0.789 | Less Dense |
| Water (4°C) | 1000 | 1.000 | Same Density |
| Aluminum | 2700 | 2.700 | More Dense |
| Lead | 11340 | 11.340 | More Dense |
Summary
Comparing relative densities involves assessing whether a substance's relative density value is less than, greater than, or equal to 1. This tells you if the substance is less dense, more dense, or has the same density as the reference material.
